Hydrocarbon fluid thermophysical property measurement under native or in-situ conditions is a critical part of estimating the economic values of a subterranean formation reservoir. Among the fluid thermophysical properties of interest is viscosity, which is the characteristic of a fluid to dissipate energy. The viscosity of a formation fluid can help identify the type of petroleum (e.g., heavy oil, medium oil, light oil) present in the formation. However, the viscosity of a hydrocarbon fluid is also strongly dependent upon temperature and pressure. Viscosity measurements may be performed by exposing a vibrating tube or wire-based sensing device to a downhole fluid to be measured and causing the sensing device to vibrate within the fluid. By measuring the loading effects of the fluid on the vibration of the tubing or the wire, the viscosity of the downhole fluid may be determined. On the other hand, hydrocarbon producing wells may contain different phases and mixtures, each having different thermophysical properties. During petroleum production operations, thermophysical properties, such as density and viscosity, and other parameters often affect production efficiency. High viscosity hydrocarbon fluid production may require external heating to reduce the viscosity of the fluid and enable fluid transport from one place in the reservoir to the well location. It is thus desirable to be able to measure viscosity properties during wireline logging service or during the production process. The obtained formation fluid viscosity property can be used for wellbore completion, production efficiency control, and optimization.
Viscosity is the internal resistance to flow exhibited by a fluid, and is a key fluid parameter for a variety of fluids, including lubricants, adhesives, paints, oils, tars, electrophoresis gels, syrups and fuels. Various methods have been developed to measure viscosity, including capillary force, moving paddles, blades, vibrating tuning forks, and hollow tubes or cantilevers immersed in a fluid. More recently, rheometers and viscometers have been developed with a vibrating micro-machined silicon cantilever that is immersed in the fluid of interest, with the resultant damping of the cantilever vibration being used to indicate viscosity. The above-noted solutions have performed satisfactorily in the laboratory, but have proven challenging to implement in a downhole high-temperature and high-pressure (HTHP) harsh environment. It is therefore desirable to have a high-sensitivity viscosity sensing device that can reliably operate under downhole harsh environmental conditions.